Power Grids
FIGS. 1-4 illustrate related art disclosed in U.S. Pat. No. 8,002,592. FIG. 1 shows a transmission tower 200 which is used to suspend power transmission lines 202 above the ground. The tower 200 has cantilevered arms 204. Insulators 206 extend down from the arms 204. One or more suspension clamps 208 are located at the bottom ends of the insulators 206. The lines 202 are connected to the suspension clamps. The clamps 208 hold the power transmission lines 202 onto the insulator 206.
FIGS. 2-4 illustrate an example of the suspension clamp 208 which generally comprises an upper section 210 and a lower support section 212. These two sections 210, 212 each contain a body 214, 216 which form a suspension case. The bodies 214, 216 each comprise a longitudinal trough (or conductor receiving area) 215, 217 that allow the transmission conductor 202 to be securely seated within the two sections and when the two sections are bolted (or fastened) together by threaded fasteners 201 (not shown). This encases the transmission conductor 202 between the two bodies to securely contain the transmission conductor 202 on the clamp 208. Threaded fasteners are not required and any other suitable fastening configuration may be provided.
The two bodies 214, 216 connected together are suspended via a metal bracket 218 that attaches to the lower body 216 at points via bolt hardware 220.
The lower body, or lower body section, 216 comprise a first end 219 and a second end 221. The conductor receiving area (or conductor contact surface) 217 extends from the first end 219 to the second end 221 along a top side of the lower body 216. The conductor receiving area 217 forms a lower groove portion for contacting a lower half of the conductor 202. A general groove shape is not required, and any suitable configuration may be provided.
In one implementation, the upper and lower sections 210, 212 each have imbedded within their respective bodies 214, 216 one-half of a current transformer 222, 224 that is commonly referred to in the industry as a split core current transformer. When these components 222, 224 are joined, they form an electromagnetic circuit that allows, in some applications, the sensing of current passing through the conductor 202. In one implementation, the current transformer is used to power sensing, data collection, data analysis and data formatting devices. In some implementations the current transformer may be located outside of the clamp or similar device or, in some implementations, power may be provided by another means.
The body 214 of the upper section 210 contains a first member 232 and a second member 234 forming a cover plate. The first member 232 comprises a first end 233, a second end 235, and a middle section 237 between the first end 233 and the second end 235. The conductor receiving area (or conductor contact surface) 215 extends from the first end 233 to the second end 235 along a bottom side of the first member 232. The conductor receiving area 215 forms an upper groove portion for contacting an upper half of the conductor 202. A general groove shape is not required, and any suitable configuration may be provided. In one implementation, the first member 232 further comprises a recessed cavity 226 at the middle section 237 that effectively contains an electronic circuit 228. In this implementation, the electronic circuit 228 is designed to accept inputs from several sensing components. This cavity 226 may be surrounded by a faraday cage 230 to effectively nullify the effects of high voltage EMF influence from the conductor 202 on the circuitry 228. The faraday cage may also surround the current transformer 222. The cover plate, or cover plate member, 234 can cover the top opening to the cavity 226 to retain the electronic circuit inside the body, or upper body section, 214. The electronics may be housed in a metal or plastic container, surrounded by the noted faraday cage, and the entire assembly can be potted, such as with epoxy for example.
The electronic circuit 228 can accept and quantify in a meaningful manner various inputs for monitoring various parameters of the conductor 202 and the surrounding environment. The inputs can also be derived from externally mounted electronic referencing devices/components. The inputs can include, for example: Line Current reference (as derived from the Current transformer 222, 224 or other means); Barometric pressure and Temperature references—internal and ambient (as derived from internal and external thermocouples 236, 238 or other means); Vibration references of the conductor (as derived from the accelerometer 240, such as a 0.1 Hz to 128 Hz vibration sensor, for example, or other means); and Optical references (as derived from the photo transistor 242 in a fiber optic tube or other means). The optical reference portion may, for example, allow the clamp to look up and see flashes of light from corona if the insulator starts to fail, or lightening indication storm activity, and/or tensile references (as derived from the tension strain device 244 which may be included in certain implementations). The tensile references from the tensile indicators 244 may, for example, provide information indicating that ice is forming as the weight of the conductor increases due to ice build up.
Supervisory Control And Data Acquisition (SCADA) generally refers to an industrial control system such as a computer system monitoring and controlling a process. Information derived by the electrical/electronic circuitry can exit the circuit 228 via a non-conductive fiber optic cable 246 and be provided up and over to the transmission tower 200 and ultimately at the base of the tower and fed into the user's SCADA system to allow the end user to access and view electrical and environmental conditions at that sight, or the information can be transmitted to a remote or central site. This implementation, however, has proven to be problematic. For example, routing fiber to a clamp that is operating at very high voltage creates a voltage creep path that can cause an arc even though glass fiber and plastic sheath are provided as insulators. Arcs form along the boundary between the air and the solid insulator. If the insulator were just a simple rod, it would have to be 3 times longer. The suspension clamp or other sensing device may be alternatively configured to wirelessly transmit information from the electronic circuit 228 to a receiver system. However, this implementation has likewise been problematic due to the complexity of the software needed to accommodate the distances over which the clamps are used and the number of clamps being monitored.
Certain Problems can Occur in Current Grids
Transmission lines face numerous problems. Wind causes vibration which can gradually crack the wire or destroy it outright. Excessive heat may cause lines to sag into trees or traffic. Corroded wires will generate more heat when current passes through, but there is no way to know the extent of any corrosion since it is generally interior to the wire. Corona is a type of electrical discharge which will eat away at wire, insulators, and anything else in the vicinity. Ice buildup can break wire due to the weight. Trees may fall naturally over wires and pose a hazard if not trimmed. Natural and man-made disasters, such as earthquakes and forest fires can damage transmission power lines. In addition, wildlife, and squirrels in particular, can get carbonized when they crawl into certain components of a power grid, thereby causing disruption of power transmission via the power transmission lines. Further, environmental elements such as wind can impact low capacity of a conductor. Wind speed and the associated temperature of a conductor affects current throughput and therefore grid planning. Line optimization to boost capacity is temperature dependent and can currently only be done via conservative estimates of local conditions due to lack of effective systems and methods for detecting the cooling effects of wind on conductors. A need therefore exists for a more accurate effective wind speed sensor that can be used to more reliably and accurately assess conditions on a conductor and its capacity in a dynamic, real-time manner.
Grid Monitoring
In conventional power grids, current and voltage are measured at substations. Current capacity of a line is estimated based on the wire diameter, age of the wire, the ambient temperature, and wind speed. However, due to many variables, it is an educated guess. In addition, there is no early warning with regard to ice build-up and ice is detected when a wire breaks during icing. Vibration dampers are routinely attached to the power lines to reduce vibration; however, their effectiveness is only estimated by how many lines break due to vibration stress, in spite of the dampers being present. The power lines can generate corona that can be heard as a sizzling sound and can also be seen by using special cameras that can see in the ultraviolet spectrum. However, such cameras are large and expensive. The cameras are generally sent to places where someone has heard a sizzling sound or where an insulator appears to be eaten away but may not be effective since corona can be intermittent and is affected by many environmental conditions such as moisture and air pressure. Further, most proposed telemonitoring devices require battery power. Battery power is not suitable in these applications that are elevated above ground and distributed over large geographic areas, making their maintenance untenable. In addition to powering challenges, existing monitoring devices are relatively expensive and large, which limits their use to occasional applications or installation to limited sites. As a result, there is no opportunity to gather widespread data and make determinations such as lightning location by way of triangulation or real-time power carrying capacity based upon full transmission line weather conditions.
Repair or Servicing a Transmission Line
Initially, one must locate where a power transmission line is broken. However, power transmission lines can run hundreds of miles between substations, and the only information generally available is that one substation is supplying power and the next one is not receiving the supplied power. Accessibility to power transmission lines may vary. In some cases, the power transmission lines may be accessible by motorized ground vehicles. In other cases, lines may only be accessible by helicopter, wherein a service technician must hang under the helicopter to service or repair a line. Such repairs or maintenance can be very expensive. A need therefore exists for systems and methods for monitoring conductors in a predictive and real-time manner.
Communication Issues
In order to retrieve information about the system, rapid and secure communication is necessary. Radio communication via Ethernet is one option. However, organizing an Ethernet network requires the use of devices known as routers or switches. Each router or switch will look at an Ethernet packet of information and make note of the source address and the destination address as the packet arrives at a port. If the destination is known, the packet is forwarded to only one port which is known to be connected to that destination device. If it is not a known address, it is repeated to all ports except the port where it arrived. When the destination device responds, the source address will appear in a packet on a single port which permit the router or switch to learn where to send the next packet with that particular destination address.
There are specific protocols which optimize the route for delivering a packet and to remove the opportunity for a packet to become repeated in a loop in the network. Some of the more common protocols are Spanning Tree Protocol and Rapid Spanning Tree Protocol.
A popular radio protocol for packet-based transmission is Zigbee which is described in standard IEEE 802.15.4. It is intended for relatively small radio networks in a small geographic area. It is well suited to a single building or a property of several acres. However, when the radios become numerous and spread out over a large area, the system becomes unworkable. The most distant radio message must be repeated by coordinator elements (e.g., a more capable radio) until the destination is reached. Because there is a time limit for a reply, the physical dimensions of the network are limited.
Although devices exist for monitoring transmission lines, they face the powering, diagnostic and communication challenges noted above. There is a need for a system that allows for fast analysis of any actual or potential repair problems and power optimization capabilities along transmission lines (e.g., to permit, for example, increased peak loads based upon real operating conditions versus conservative estimates based upon worst case weather), with lower costs of repair, better preventative maintenance, and faster restore times. Further, there is a need for a simple way of communicating and collecting the substantial amount of data that can be accumulated by a wide-spread installation of sensing devices over large geographic areas.
Wind Determination
Power transmission lines and other conductors can heat up due to current passing through the lines. A current limit on a line can be affected by the temperature of the line. Further, the line temperature can depend on the current through the line, the electrical resistance of the line (usually defined by the diameter of the conductor), the ambient temperature, the wind speed, and the direction of the wind. For example, a small wind blowing directly across a wire, such as a 2-mph wind, can provide significant cooling effect, and can increase a current capacity of the line. A wind blowing along the wire will be less effective at cooling. While some formulas exist to determine the effectiveness of wind in cooling a conductor, these formulas are not as accurate as desired.
A conventional wind speed meter, the hot wire anemometer, measures ambient temperature and heats a small wire (typically with a 5 mil diameter) often made from nickel chromium. The resistance of the wire varies with temperature. Accordingly, resistance measurement is typically used to obtain the temperature of the wire. The temperature can vary with the wind speed. The hot wire anemometer uses a table or formula to convert temperature difference (hot wire temperature−ambient temperature) to wind speed. The wire in a hot wire anemometer is far too fragile to be used in an application such as measuring effective wind speed on a power line, which is sometimes exposed to harsh environmental conditions. Thus, this conventional wind speed meter is extremely fragile and is not workable in most conditions on power transmission lines and other conductors.